The Critical Path Method (CPM) is an algorithm used to plan a set of project activities, its purpose is to highlight the steps involved in the longest path that determines the project end date.

To use this method, you must build the model by paying attention to:

Define all projects’s phases

Highlight dependencies between phases

Calculate the duration of each phase correctly

The critical path analysis allows you to highlight what activities are “critical” but also those that can be delayed without increasing the project lifespan.

If you have never used this methodology, let’s try to apply it to a simple example: imagine we have to install a shelf in the house.

First, you need to split the project into phases:

Buy the shelf

Buy the fixing bars

Choose the wall and the height

Make the signs on the wall

Do the holes with the drill

Install the fixing bars

Mount the shelf

Once you define each steps, you can try to identify the dependencies: at a first analysis you immediately realize that some activities can not be started until others are completed, for example, you can not do holes with the drill until you make the signs on the wall, also the shelf can not be placed until the fixing bars are fixed. At the same time you see that the choice of the wall, the purchase of the shelf and fixing bars are activities that you can do in parallel. Here is the Gantt of activities with dependencies:

This type of activity can be easily planned using the Gantt diagrams that also shows the critical path calculation in red. The chart shows the sequential activities, they are in orange because suspended waiting for predecessor completion.

All these sequential activities are the fundamental steps that determine the length of your project. The critical path of the projects is the longest sequence of activities.

It is essential to pay close attention to phases on the critical path to manage the timing of your Gantt. For example, if you have a task that lasts 100 days, a 5-day delay on one of the sequential activities will result in a total delay of 5 days for the task.

Another important aspect to consider is the human resources availability, for example, we have said that some phases can be done in parallel such as buying fixing bars, shelf and choosing height in the wall, but these can be done in parallel only if you can count on three different resources available, in case you are alone to complete the project the Gantt changes drastically. Phases become all consecutive.

So, project critical path can be calculated according to tasks dependencies, but to determine task end dates it is necessary to identify the resources at your disposal and the correct duration of each phase. Only after analyzing these two aspects will you be able to handle project times by using a Gantt diagram and see a correct schedule.

From this simple example it is clear that critical path analysis is not trivial, this method is particularly used for complex but predictable activities.

In the real world, in fact, it is difficult to follow exactly the established plan, moreover, you can have external new requirements or constraints not considered at an early stage of planning.

In our example, if you did not find the fixing bars in the store and you have to order them online you could introduce a delay that could reflect on the overall project’s duration, even if this phase was not in the critical path.

Conclusion:

To keep track of the progress of your plan, you must:

Update your data frequently.

Carefully monitor the steps on the critical path, but also the ones outside.

Keep the availability of resources under control.

That’s why, relying on a software that manages easy-to-update Gantt diagrams, it’s crucial to quickly add dependencies, as shown in the previous images, but also to include phases duration and calculate the end date automatically. An interactive Gantt diagram will also allows you to quickly re-schedule tasks.

If you rely on a project management software such as Twproject, which includes, in addition to the interactive Gantt with critical path analysis, also a tool to monitor resources, you can easily manage the load to provide the flexibility you need to act promptly on any critical issues and finally have everything under control.